The invention relates to placement of tubular endoprostheses or stents for body passages, particularly for opening, dilating and maintaining blood vessels and other biological ducts which are at risk of closure due to flaps, dissections, loose vessel debris, etc.
The general use of endoprostheses for such purposes is well known. In one technique a tubular endoprosthesis is mounted over an inflatable balloon of corresponding length, which is part of a disposable balloon catheter. The catheter is inserted into a vessel or duct and guided to the desired site. The balloon is then expanded to expand and permanently secure the endoprosthesis at the site. After this the balloon is deflated and the catheter is withdrawn to complete the placement sequence, and the balloon catheter is discarded. When the region of the blood vessel or duct requires placement over a length greater than the length of a standard prosthesis, often two of the prostheses are placed by their respective balloon catheters in end-to-end relationship with some overlap. This requires two separate placement sequences, requires the use of two disposable balloon catheters, and creates a number of problems both in placement and in use. Other techniques seeking to use long endoprostheses and stents have had drawbacks related to placement or use.
I have provided a long tubular endoprosthesis which is longer than its expansion balloon, and have provided for selective inflation, deflation, axial shifting of position and reinflation of the inflation balloon to progressively expand the endoprosthesis to place it in a duct or vessel section. In particularly preferred embodiments the endoprosthesis is a stent of knitted construction.
More particularly, according to one aspect of the invention, I provide a method and device for implanting an endoprosthesis within the lumen of a body passageway comprising providing a tubular shaped, elongated endoprosthesis having a small first diameter which permits intraluminal delivery of the endoprosthesis into a selected body passageway, the endoprosthesis being capable of being progressively permanently deformed to an expanded diameter upon application of radial, outwardly acting force applied to the interior wall of the endoprosthesis; providing a catheter having an inflatable, radially expandable portion, the axial dimension of which is shorter than the axial dimension of the endoprosthesis; inserting the elongated prothesis in unexpanded state into a desired location within the body passageway; with the catheter positioned within the endoprosthesis so that its expandable portion registers with a first portion of the endoprosthesis, inflating the inflatable portion of the catheter to cause the deformation of the first portion of the endoprosthesis to a second, expanded diameter; causing the deflation of the inflatable portion of the catheter; axially shifting the inflatable portion of the catheter within the endoprosthesis while the inflatable portion is in deflated state until the inflatable portion registers with an unexpanded portion of the endoprosthesis; and repeating the inflation of the inflatable portion of the catheter at least one additional time until the elongated endoprosthesis is expanded throughout the desired length, and the endoprosthesis is permanently placed in supporting relationship within the lumen of the body passageway; and thereafter withdrawing the catheter.
Preferred embodiments of this aspect of the invention have one or more of the following features.
Prior to insertion of the endoprosthesis into the body, the elongated endoprosthesis is mounted in unexpanded state over the inflatable portion of the catheter, the inflatable portion of the catheter being in deflated state. The catheter is then inserted into the body to place the endoprosthesis in the desired location.
The first portion of the endoprosthesis has an initial unexpanded diameter smaller than the unexpanded diameter of remaining portions of the endoprosthesis such that the initial diameter of the first portion secures the endoprosthesis upon the expandable portion of the catheter for insertion, and the diameter of the remaining portions of the endoprosthesis enables the catheter, after expansion of the first portion of the endoprosthesis, to be moved axially within the endoprosthesis when the inflatable portion is in at least a partially deflated state.
Alternatively, the endoprosthesis in unexpanded state is of uniform size and is detachably secured over the inflatable portion prior to insertion into the body.
In one preferred embodiment, the endoprosthesis is secured by partially inflating the inflatable portion sufficiently to secure the endoprosthesis to the catheter prior to insertion into the body.
The long endoprosthesis is preferably of knitted construction enabling it to conform to tortuosities of the duct.
According to another aspect of the invention, a medical device is provided comprising a tubular shaped, elongated knitted stent having a small first diameter which permits intraluminal delivery of the stent into a selected body passageway, the stent being capable of progressive permanent deformation to an expanded diameter upon application of radial, outwardly acting force applied to the interior wall surface of the stent; a catheter having an inflatable, radially expandable portion associated therewith, the axial dimension of which being shorter than the axial dimension of the stent; the elongated stent being detachably mounted in unexpanded state on the catheter with the inflatable portion of the catheter disposed within a first portion of the stent which is to be first expanded.
Furthermore, according to the present invention, I have realized that disadvantages of prior techniques can be overcome by employing a longer than usual endoprosthesis and an axially movable balloon intentionally substantially shorter than the endoprosthesis. The same balloon is then employed to inflate different sections of the endoprosthesis, by axially shifting the balloon within the endoprosthesis between inflations.
Prior art expandable tubular endoprostheses, and in particular vascular stents, have often ranged from 2-14 mm diameter and generally have been limited to about 8 cm in length because of limits on practical balloon length. As the length of the balloon increases, uniform balloon expansion is difficult to achieve, and if the balloon is too long it will cause the endoprosthesis to be expanded in a non-uniform, undesirable way.
One of the advantages of the technique I have provided is that it can ensure uniform expansion throughout the length of a long endoprosthesis. Another advantage is avoiding the time-consuming step of overlapping one endoprosthesis over the next. Avoidance of overlap furthermore avoids rigidity and reduced flexibility of the endoprosthesis at the region of the overlap, and therefore avoids differences in compliance created along the length of the vessel. Differences in compliance have been shown by vascular surgeons to create areas where stenosis becomes more aggressive. The invention can also avoid a decrease in the diameter of the lumen at the overlap which may present blood flow abnormalities and lead to increased likelihood of thrombosis. The invention also eliminates the need, after each section of endoprosthesis is positioned, to remove the catheter from the patient""s body and insert a new catheter and endoprosthesis and thus can reduce the duration of the procedure and the patient""s risk of infection.
According to the invention, a balloon of standard length may be employed to place any length endoprosthesis. The surgeon simply inflates the balloon to dilate one section of the endoprosthesis, deflates the balloon, moves the balloon distally a distance slightly short of one balloon length, then reinflates the balloon, and repeats this procedure until the entire length of the endoprosthesis is expanded. Such a standard length balloon can be selected to be relatively short, which can facilitate placement of long endoprostheses to severely tortuous pathways. Placement in such tortuous pathways is particularly effective when the stent is of knitted construction.